# Can I use low voltage but higher maximum amperage?

I have an electronic device (electromagnet solenoid) that working on 9V/DC and 30mA current (9*30=270mW)

Question 1: If there is a 5V/DC adapter that could produce maximum 54mA (5*54=270mW), could I use it to power that solenoid?

Question 2: Does the high voltage low current is same as low voltage high current , alhough they produce the same Watt?

• Consider the resistance of the coil and the equation V=IR. Note that the resistance will stay the same when you change the voltage, so what happens to the current? – Andrew Morton Oct 11 '17 at 7:52

No. Current and Voltage are two different things. Related perhaps, but different.

The solenoid needs a certain amount of current flowing through it for it to activate. The properties of your particular solenoid means that, in order for 30 mA to flow, you must supply 9 volts to its terminals. Connecting 5 volts will not help.

You can also use a constant current source instead of a voltage source. It is simply a circuit that makes sure that 30 mA of current flows, no matter what (up to practical limits set by the designer). If you use such a current source on your solenoid, your current source will quickly find the right voltage so that 30 mA flows, and this will be 9 volts.

You can design a circuit that converts your 5 volt output to a 9 volt output. Then it is useful to know the "wattage" of the supply, because it must still be able to drive the solenoid.

The resistance of the solenoid determines the current draw at a particular voltage, not the power supply. It is possible that the solenoid would operate properly at 5V but the current draw would be less than when operating at 9V, not more.

The resistance of the coil is probably 300 ohms (R = E/I -> 9V/30mA). At 5V the coil will draw 16mA which is 83mW. That is unlikely to be enough to activate the solenoid.

• I have a 5v dc adapter that could produce maximum 1A, could I use the step up converter to 9 volt and power it? I read that If you double the voltage, the current output will be dropped by a half. – Zynskav Zynskav Oct 11 '17 at 8:03
• Yes, as long as it can provide 30mA at 9V the solenoid will work as expected. – Dean Franks Oct 11 '17 at 8:33